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E-RAB Release Request

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The E-RAB (Evolved Radio Access Bearer) Release Request procedure in LTE (Long-Term Evolution) and 5G wireless networks is initiated to release an established dedicated bearer, which is a communication path between the user equipment (UE) and the core network. The procedure involves signaling exchanges between the UE, the eNodeB (in LTE), or the gNodeB (in 5G), and the core network entities. Here's a technical explanation of the E-RAB Release Request procedure:

1. E-RAB Release Trigger:

  • UE Request: The E-RAB Release Request procedure can be initiated by the UE when it no longer requires the dedicated bearer, such as when a data session is complete.
  • Network-Initiated: Alternatively, the network may initiate an E-RAB release due to handovers, policy changes, or network optimizations.

2. UE Signaling:

  • UE-to-eNodeB/gNodeB Message: If the UE initiates the release, it sends an E-RAB Release Request message to the serving eNodeB (in LTE) or gNodeB (in 5G). This message contains information about the E-RAB to be released, such as its identifier.
  • Release Reason: The message may also include a release cause, indicating the reason for the release (e.g., normal release, handover, UE requested).

3. eNodeB/gNodeB Processing:

  • Message Handling: The eNodeB/gNodeB receives the E-RAB Release Request message from the UE and processes it.
  • Release Validation: The eNodeB/gNodeB verifies the validity of the release request, ensuring that it pertains to an established E-RAB and that the request aligns with network policies.

4. E-RAB Release Signaling:

  • Release Request to MME: If the eNodeB/gNodeB determines that the release request is valid, it forwards the E-RAB Release Request message to the Mobility Management Entity (MME) in the core network.
  • Release Cause Forwarding: The eNodeB/gNodeB includes information about the release cause in the message to the MME, indicating the reason for the release.

5. MME Handling:

  • Release Confirmation to Core Network: The MME processes the E-RAB Release Request message received from the eNodeB/gNodeB and verifies the release request.
  • Resource Deallocation: The MME initiates the deallocation of resources associated with the E-RAB within the core network and informs relevant network elements, including the Serving Gateway (S-GW) and Packet Data Network Gateway (P-GW), to release their resources.

6. E-RAB Release Confirmation:

  • MME Confirmation to eNodeB/gNodeB: Once the MME has successfully deallocated the resources and verified the E-RAB release, it sends an E-RAB Release Response message to the eNodeB/gNodeB.
  • Release Confirmation to UE: The eNodeB/gNodeB receives the E-RAB Release Response message and forwards it to the UE. This confirms the successful release of the E-RAB.

7. UE State Transition:

  • UE Response: Upon receiving the E-RAB Release Response message, the UE transitions its internal state accordingly. The UE releases any remaining resources associated with the E-RAB and updates its context.

8. Continued Operation:

  • Post-Release Operation: After the E-RAB Release Request procedure, the UE can continue its communication, establish new E-RABs if needed, or transition to a different operational state based on the network's requirements.

The E-RAB Release Request procedure is crucial for efficiently managing network resources and ensuring that communication resources are released when no longer needed. It allows for the graceful termination of communication sessions and is an essential part of LTE and 5G network operation.